While ASR provides pilots with horizontal guidance
for instrument approaches via a ground-based radar,
Precision Approach Radar (PAR) provides both horizontal
and vertical guidance for a ground controlled
approach (GCA). In the U.S., PAR is mostly used by
the military. Radar equipment in some ATC facilities
operated by the FAA and/or the military services at
joint-use locations and military installations are used
to detect and display azimuth, elevation, and range of
aircraft on the final approach course to a runway.
This equipment may be used to monitor certain nonradar
approaches, but it is primarily used to conduct
a precision instrument approach.

BRIGHT RADAR INDICATOR TERMINAL EQUIPMENT

Bright Radar Indicator Terminal Equipment (BRITE)
provides radar capabilities to towers, a system with
tremendous benefits for both pilots and controllers.
Unlike traditional radar systems, BRITE is similar to a
television screen in that it can be seen in daylight.
BRITE was so successful that the FAA has installed the
new systems in towers, and even in some TRACONs. In
fact, the invention of BRITE was so revolutionary that
it launched a new type of air traffic facility ? the
TRACAB, which is a radar approach control facility
located in the tower cab of the primary airport, as
opposed to a separate room.

In the many facilities without BRITE, the controllers
use strictly visual means to find and sequence traffic.
Towers that do have BRITE may have one of several different types. Some have only a very crude display
that gives a fuzzy picture of blips on a field of green,
perhaps with the capability of displaying an extra slash
on transponder-equipped targets and a larger slash
when a pilot hits the ident button. Next in sophistication
are BRITEs that have alphanumeric displays of
various types, ranging from transponder codes and altitude
to the newest version, the DBRITE (digital
BRITE). A computer takes all the data from the primary
radar, the secondary radar (transponder information), and
generates the alphanumeric data. DBRITE digitizes the
image, and then sends it all, in TV format, to a square display
in the tower that provides an excellent presentation,
regardless of how bright the ambient light.

One of the most limiting factors in the use of the BRITE
is in the basic idea behind the use of radar in the tower.
The radar service provided by a tower controller is not,
nor was it ever intended to be, the same thing as radar
service provided by an approach control or Center. The
primary duty of tower controllers is to separate airplanes
operating on runways, which means controllers spend
most of their time looking out the window, not staring at
a radar scope.

RADAR COVERAGE

A full approach is a staple of instrument flying, yet
some pilots rarely, if ever, have to fly one other than
during initial or recurrency or proficiency training,
because a full approach usually is required only when
radar service is not available, and radar is available at
most larger and busier instrument airports. Pilots come
to expect radar vectors to final approach courses and
that ATC will keep an electronic eye on them all the
way to a successful conclusion of every approach. In
addition, most en route flights are tracked by radar
along their entire route in the 48 contiguous states,
with essentially total radar coverage of all instrument
flight routes except in the mountainous West. Lack of
radar coverage may be due to terrain, cost, or physical
limitations.

New developing technologies, like ADS-B, may offer
ATC a method of accurately tracking aircraft in nonradar
environments. ADS-B is a satellite-based air
traffic tracking system enabling pilots and air traffic
controllers to share and display the same information.
ADS-B relies on the Global Positioning System (GPS)
to determine an aircraft’s position. The aircraft’s precise
location, along with other data such as airspeed,
altitude, and aircraft identification, then is instantly
relayed via digital datalink to ground stations and other
equipped aircraft. Depending on the location of the
ground based transmitters (GBT), ADS-B has the
potential to work well at low altitudes, in remote locations,
and mountainous terrain where little or no radar
coverage exists.